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| United States Patent |
5,741,618
|
|
Shigemori
, et al.
|
April 21, 1998
|
Process for producing polymer toner
Abstract
A process for producing a polymer toner comprises the steps of pouring a
polymerizable monomer composition containing at least a polymerizable
monomer and a colorant, but containing no oil-soluble polymerization
initiator into an aqueous dispersion medium containing a dispersing agent;
adding an oil-soluble polymerization initiator to the polymerizable
monomer composition while stirring the composition to form primary
droplets thereof, thereby bringing the droplets of the polymerizable
monomer composition into contact with droplets of the oil-soluble
polymerization initiator to form droplets of a polymerizable monomer
composition containing the oil-soluble polymerization initiator; further
continuing the stirring to form secondary droplets having desired droplet
sizes; and then conducting suspension polymerization of the polymerizable
monomer composition.
| Inventors:
|
Shigemori; Kazunori (Kanagawa-ken, JP);
Ogawa; Tokudai (Kanagawa-ken, JP)
|
| Assignee:
|
Nippon Zeon Co. Ltd. (JP)
|
| Appl. No.:
|
728475 |
| Filed:
|
October 10, 1996 |
Foreign Application Priority Data
| Current U.S. Class: |
430/137.17; 430/109.3; 523/223; 524/779; 524/832; 524/836 |
| Intern'l Class: |
G03G 005/00 |
| Field of Search: |
430/137,109
523/223
524/779,832,836
|
References Cited
U.S. Patent Documents
| 4077804 | Mar., 1978 | Vanzo | 430/137.
|
| 4330460 | May., 1982 | Hoffend et al. | 524/849.
|
| 4601968 | Jul., 1986 | Hyosu | 430/137.
|
| 4626489 | Dec., 1986 | Hyosu | 430/137.
|
| 4804610 | Feb., 1989 | Mori et al. | 430/137.
|
| 5130220 | Jul., 1992 | Nakamura et al. | 430/137.
|
| 5217839 | Jun., 1993 | Yamada et al. | 430/137.
|
| 5427885 | Jun., 1995 | Ota et al. | 430/137.
|
| Foreign Patent Documents |
| 59-123852 | Jul., 1984 | JP | 430/137.
|
Primary Examiner: Lesmes; George F.
Assistant Examiner: VerSteeg; Steven H.
Attorney, Agent or Firm: Armstrong, Westerman, Hattori, McLeland & Naughton
Claims
We claim:
1. A process for producing a polymer toner, which comprises the steps of:
pouring a polymerizable monomer composition (A) containing at least a
polymerizable monomer and a colorant, but containing no oil-soluble
polymerization initiator, into an aqueous dispersion medium containing a
dispersing agent;
stirring the aqueous dispersion medium to form primary droplets of the
polymerizable monomer composition (A) therein;
adding an oil-soluble polymerization initiator to the aqueous dispersion
medium, at the time the volume average droplet size of the primary
droplets comes to a droplet size within a range of 50-1,000 .mu.m, while
stirring the aqueous dispersion medium, thereby bringing the primary
droplets into contact with droplets of the oil-soluble polymerization
initiator to form droplets of the resulting polymerizable monomer
composition (B) containing the oil-soluble polymerization initiator;
further stirring the aqueous dispersion medium to form secondary droplets
of the polymerizable monomer composition (B) having a desired droplet
size; and then
conducting suspension polymerization of the polymerizable monomer
composition (B).
2. The process according to claim 1, wherein the polymerizable monomer
comprises a crosslinkable monomer in a proportion of 20 wt. % or lower.
3. The process according to claim 1, wherein the polymerizable monomer
comprises a styrene monomer, a (meth)acrylic ester and an aromatic divinyl
compound.
4. The process according to claim 1, wherein the dispersing agent is
colloid of a hardly water-soluble polyvalent metal hydroxide formed by the
reaction of a water-soluble polyvalent metal salt with an alkali metal
hydroxide in water.
5. The process according to claim 1, wherein the oil-soluble polymerization
initiator has a solubility in water of 1 wt. % or lower.
6. The process according to claim 1, wherein the oil-soluble polymerization
initiator is a peroxide or azo oil-soluble initiator.
7. The process according to claim 1, wherein the oil-soluble polymerization
initiator is an organic peroxide whose ten-hour half-life temperature is
60.degree.-80.degree. C. and whose molecular weight is 250 or lower.
8. The process according to claim 1, wherein the secondary droplets are
formed so as to have droplet sizes within a range of 1-50 .mu.m.
9. The process according to claim 1, wherein the secondary droplets are
formed so as to have droplet sizes within a range of 5-30 .mu.m.
10. A process for producing a polymer toner, which comprises the steps of:
pouring a polymerizable monomer composition (A) containing at least a
polymerizable monomer and a colorant, but containing no oil-soluble
polymerization initiator, into an aqueous dispersion medium containing a
dispersing agent;
stirring the aqueous dispersion medium to form primary droplets of the
polymerizable monomer composition (A) therein;
adding an oil-soluble polymerization initiator to the aqueous dispersion
medium at the time the volume average droplet size of the primary droplets
come to a droplet size within a range of 100-500 .mu.m, while stirring the
aqueous dispersion medium, thereby bringing the primary droplets into
contact with droplets of the oil-soluble polymerization initiator to form
droplets of the resulting polymerizable monomer composition (B) containing
the oil-soluble polymerization initiator;
further stirring the aqueous dispersion medium to form secondary droplets
of the polymerizable monomer composition (B) having a desired droplet
size; and then
conducting suspension polymerization of the polymerizable monomer
composition (B).
11. A process for producing a polymer toner, which comprises the steps of:
pouring a polymerizable monomer composition (A) containing at least a
polymerizable monomer and a colorant, but containing no oil-soluble
polymerization initiator into an aqueous dispersion medium containing a
dispersing agent, which is a colloid of a hardly water-soluble polyvalent
metal hydroxide formed by the reaction of a water-soluble polyvalent metal
salt, which is at least one selected from the group consisting of
magnesium salts and calcium salts, with an alkali metal hydroxide, which
is at least one selected from the group consisting of sodium hydroxide,
lithium hydroxide and potassium hydroxide, in water;
stirring the aqueous dispersion medium to form primary droplets of the
polymerizable monomer composition (A) therein;
adding an oil-soluble polymerization initiator to the aqueous dispersion
medium while stirring the aqueous dispersion medium, thereby bringing the
primary droplets into contact with droplets of the oil-soluble
polymerization initiator to form droplets of the resulting polymerizable
monomer composition (B) containing the oil-soluble polymerization
initiator;
further stirring the aqueous dispersion medium to form secondary droplets
of the polymerizable monomer composition (B) having a desired droplet
size; and then
conducting suspension polymerization of the polymerizable monomer
composition (B).
12. The process according to claim 11, wherein the dispersing agent is
colloid of hardly water-soluble magnesium hydroxide formed by the reaction
of a water-soluble magnesium salt with sodium hydroxide in water.
13. A process for producing a polymer toner, which comprises the steps of:
pouring a polymerizable monomer composition (A) containing at least a
polymerizable monomer and a colorant, but containing no oil-soluble
polymerization initiator, into an aqueous dispersion medium containing a
dispersing agent;
stirring the aqueous dispersion medium to form primary droplets of the
polymerizable monomer composition (A) therein;
adding an oil-soluble polymerization initiator, which is at least on
selected from the group consisting of t-butyl peroxy-2-ethylhexanoate,
succinamide peroxide, t-hexyl peroxy-2-ethylhexanoate and t-butyl
peroxyisobutyrate, to the aqueous dispersion medium while stirring the
aqueous dispersion medium, thereby bringing the primary droplets into
contact with droplets of the oil-soluble polymerization initiator to form
droplets of the resulting polymerizable monomer composition (B) containing
the oil-soluble polymerization initiator;
further stirring the aqueous dispersion medium to form secondary droplets
of the polymerizable monomer composition (B) having a desired droplet
size; and then
conducting suspension polymerization of the polymerizable monomer
composition (B).
14. A process for producing a polymer toner, which comprises the steps of:
pouring a polymerizable monomer composition (A) containing at least a
polymerizable monomer and a colorant, but containing no oil-soluble
polymerization initiator, into an aqueous dispersion medium containing a
dispersing agent;
stirring the aqueous dispersion medium to form primary droplets of the
polymerizable monomer composition (A) therein;
adding an oil-soluble polymerization initiator to the aqueous dispersion
medium, and controlling the temperature of the aqueous dispersion medium
within a range of 10.degree.-40.degree. C., while stirring the aqueous
dispersion medium, thereby bringing the primary droplets into contact with
droplets of the oil-soluble polymerization initiator to form droplets of
the resulting polymerizable monomer composition (B) containing the
oil-soluble polymerization initiator;
further stirring the aqueous dispersion medium to form secondary droplets
of the polymerizable monomer composition (B) having a desired droplet
size; and then
conducting suspension polymerization of the polymerizable monomer
composition (B).
Description
FIELD OF THE INVENTION
The present invention relates to a process for producing a toner for
developing electrostatic latent images to be used in electrophotography,
electrostatic recording, electrostatic printing, etc., and more
particularly to an improved process for producing colored particulate
polymer (polymer toner) by a suspension polymerization method.
BACKGROUND OF THE INVENTION
In an electrophotographic process, an electrostatic latent image is formed
on a photosensitive member (a photoconductor) evenly charged by exposure
to a light pattern, and colored, charged particles (toner) are applied to
the electrostatic latent image to make a visible image (toner image). The
toner image is transferred to transfer paper, and the unfixed toner image
is then fixed to the paper by a method such as heating. As the toner,
there is used a toner obtained by dispersing a colorant such as carbon
black and other additives in a thermoplastic resin and granulating the
dispersion.
As a production process of a toner to be used in the development of
electrostatic latent images, there has heretofore been known a process in
which a thermoplastic resin, a colorant and optional other additives are
fusion-mixed, the mixture is ground, and the ground product is classified
so as to obtain a particulate matter having desired particle sizes. In
this grinding method, it is necessary for the mixture of the thermoplastic
resin and the colorant to have brittleness to such an extent that it can
be easily ground. When such a mixture is actually ground at a high speed,
however, particles having a wide particle size distribution are liable to
be formed. In the case where a toner is provided as fine particles, in
particular, for the purpose of enhancing the resolution of a copied
product, fine particles ground in excess are generated in a great amount.
In order for a toner to exhibit satisfactory developing characteristics,
the toner must have a particle size distribution limited to some extent.
Therefore, classification is required for the purpose of obtaining a toner
having a desired particle size distribution from a ground product
containing a great amount of fine particles. However, its yield is poor,
and so the percent yield thereof is reduced to a great extent.
On the other hand, when a toner is produced in accordance with a suspension
polymerization method, a colored particulate polymer (polymer toner) can
be produced without a grinding step. In the suspension polymerization
method, a polymerizable monomer composition comprising a polymerizable
monomer, a colorant, an oil-soluble polymerization initiator and further
optionally a crosslinking agent, a charge control agent and other
additives dissolved or dispersed uniformly is prepared and then dispersed
in an aqueous dispersion medium containing a dispersion stabilizer by
means of a stirrer to form minute droplets of the polymerizable monomer
composition (a step of forming droplets), and the dispersion containing
the minute droplets are then heated to conduct suspension polymerization
of the polymerizable monomer composition, thereby obtaining a polymer
toner having desired particle sizes. The polymer toner obtained by the
suspension polymerization method is spherical in shape, has an even
surface and exhibits good developing characteristics. However, the
suspension polymerization method involves the following problems to be
solved.
In order for a toner to exhibit good developing characteristics, it is
desirable that the toner have a homogeneous composition and an even
particle size distribution. In order to obtain a polymer toner having a
homogeneous composition and an even particle size distribution in
accordance with the suspension polymerization method, it is necessary to
disperse the colorant and the polymerization initiator in the
polymerizable monomer to conduct polymerization, and further to evenly and
stably form droplets of the polymerizable monomer composition in the
aqueous dispersion medium to conduct polymerization. Namely, it is
necessary to disperse the additives such as the colorant in the droplets
of the polymerizable monomer composition in order to obtain a polymer
toner having uniform properties. When the suspended droplets of the
polymerizable monomer composition aggregate, or the droplet size
distribution of the droplets becomes wide, it is impossible to obtain a
polymer toner having an even particle size distribution.
Since the polymer toner obtained by the suspension polymerization method is
composed of particles formed by the polymerization of the droplets of the
polymerizable monomer composition dispersed in the aqueous dispersion
medium, its properties are greatly influenced by the state of the original
droplets. However, it has been very difficult to form homogeneous and even
droplets. In addition, the properties of the polymer toner are also
influenced by resin properties such as polymerization degree and
crosslinking degree of a polymer to be formed by the suspension
polymerization. However, it has been extremely difficult to make these
resin properties uniform at every polymer toner particle.
For example, in order to make the dispersion of the colorant in the
polymerizable monomer even, many methods such as a method of treating a
colorant and a method of adding a dispersing agent for a colorant have
heretofore been proposed. In order to make resin properties such as
polymerization degree and crosslinking degree uniform at every polymer
toner particle, however, it is necessary to evenly disperse an oil-soluble
polymerization initiator in the droplets of the polymerizable monomer
composition. In order to obtain a homogeneous polymerizable monomer
composition, there has hitherto been proposed a process comprising adding
a colorant, an oil-soluble polymerization initiator and further optionally
a crosslinking agent, a charge control agent and other additives dissolved
or dispersed uniformly to a polymerizable monomer containing a
polymerization inhibitor and then applying mechanical shearing force (for
example, by mixing in a ball mill) to the mixture, thereby uniformly
dissolving or dispersing the individual components in the polymerizable
monomer (U.S. Pat. No. 4,804,610). According to this process, a
composition with the individual components such as the oil-soluble
polymerization initiator uniformly dispersed in the polymerizable monomer
can be prepared by applying high shearing force.
However, such a process has involved problems that a partial polymerization
reaction is easy to occur from an initial stage after the preparation of
the polymerizable monomer composition in spite of the coexistence of the
polymerization inhibitor because the polymerization initiator is contained
in this composition, and that when mass treatment is carried out, in
particular, on an industrial scale, a run-away reaction tends to occur due
to heat accumulation. Accordingly, when the polymerizable monomer
composition is used to form droplets thereof and conduct suspension
polymerization, a polymer toner having ununiform resin properties is
liable to be formed.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for producing
a polymer toner having a homogeneous composition and an even particle size
distribution in accordance with the suspension polymerization method.
The present inventors have conceived of a process in which a polymerizable
monomer composition containing at least a polymerizable monomer and a
colorant, but containing no oil-soluble polymerization initiator is
prepared, and an oil-soluble polymerization initiator is then included in
the composition in an aqueous dispersion medium. According to this
process, neither partial polymerization reaction nor run-away reaction is
brought on at a stage of the preparation of the polymerizable monomer
composition because no oil-soluble polymerization initiator is added
thereto, and so a polymerizable monomer composition having a homogeneous
composition can be prepared by application of high shearing force through
stirring.
When the oil-soluble polymerization initiator is added after the
polymerizable monomer composition is formed into droplets having desired
droplet sizes in the aqueous dispersion medium, however, it is difficult
to uniformly disperse the oil-soluble polymerization initiator in the
droplets, resulting in difficulty in making resin properties such as
polymerization degree and crosslinking degree uniform at every polymer
toner particle. The term "formation into droplets having desired droplet
sizes" as used herein means that droplets are evenly, finely divided by
stirring to such an extent that in the subsequent suspension
polymerization, a polymer toner having a volume average particle size of
generally about 1-50 .mu.m, preferably about 5-30 .mu.m is formed. When
the polymerizable monomer composition is subjected to shearing force by
stirring in an aqueous dispersion medium containing a dispersing agent,
thereby being formed into such minute droplets, it is difficult to bring
the oil-soluble polymerization initiator into uniform contact with the
individual droplets to unite them when adding a small amount of the
oil-soluble polymerization initiator because a great number of the
droplets are finely dispersed and stabilized.
Therefore, the present inventors have carried out a further investigation.
As a result, it has been found that when a polymerizable monomer
composition containing no oil-soluble polymerization initiator is prepared
and poured into an aqueous dispersion medium containing a dispersing
agent, and an oil-soluble polymerization initiator is then added to the
dispersion under stirring, droplets of the composition come into contact
with droplets of the polymerization initiator to form droplets of a
polymerizable monomer composition containing the polymerization initiator.
When shearing force by stirring is applied to such droplets to form minute
droplets having desired droplet sizes, and the droplets thus formed are
heated to conduct suspension polymerization, a polymer toner homogeneous
in composition and uniform in resin properties such as polymerization
degree and crosslinking degree can be obtained.
According to this process, the droplets containing the polymerizable
monomer are brought into contact with the droplets containing the
oil-soluble polymerization initiator in the aqueous dispersion medium, so
that temperature control can be performed with ease to prevent both
partial polymerization reaction and run-away reaction. In addition, since
the minute droplets are formed by stirring under high shearing force, a
polymer toner having an even particle size distribution can be obtained.
The present invention has been led to completion on the basis of these
findings.
According to the present invention, there is thus provided a process for
producing a polymer toner, which comprises the steps of:
pouring a polymerizable monomer composition containing at least a
polymerizable monomer and a colorant, but containing no oil-soluble
polymerization initiator into an aqueous dispersion medium containing a
dispersing agent;
adding an oil-soluble polymerization initiator to the polymerizable monomer
composition while stirring the composition to form primary droplets
thereof, thereby bringing the droplets of the polymerizable monomer
composition into contact with droplets of the oil-soluble polymerization
initiator to form droplets of a polymerizable monomer composition
containing the oil-soluble polymerization initiator;
further continuing the stirring to form secondary droplets having desired
droplet sizes; and then
conducting suspension polymerization of the polymerizable monomer
composition.
According to the present invention, there are provided the following
preferred embodiments:
1. A production process wherein the primary droplets of the polymerizable
monomer composition have a volume average droplet size of 50-1,000 .mu.m,
preferably 100-500 .mu.m; and
2. A production process wherein the dispersing agent is colloid of a hardly
water-soluble polyvalent metal hydroxide formed by the reaction of a
water-soluble polyvalent metal salt with an alkali metal hydroxide in
water.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Polymerizable monomer
As the polymerizable monomer useful in the practice of the present
invention, monomers having a vinyl group are preferably used. Specific
examples thereof include vinyl monomers, such as styrene-type monomers
such as styrene, vinyltoluene and .alpha.-methylstyrene; acrylic acid or
methacrylic acid and their derivatives, such as acrylic acid, methacrylic
acid, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate,
2-ethylhexyl acrylate, ethyl methacrylate, propyl methacrylate, butyl
methacrylate, 2-ethylhexyl methacrylate, dimethylaminoethyl methacrylate,
acrylonitrile and acrylamide; ethylenically unsaturated monoolefin such as
ethylene, propylene, butylene and isobutylene; vinyl halides such as vinyl
chloride, vinylidene chloride, vinyl bromide and vinyl fluoride; vinyl
esters such as vinyl acetate and vinyl propionate; vinyl ethers such as
vinyl methyl ether and vinyl ethyl ether; vinyl ketones such as vinyl
methyl ketone and methyl isopropenyl ketone; and nitrogen-containing vinyl
compounds such as 2-vinylpyridine, 4-vinylpyridine and N-vinylpyrrolidone.
These monomers may be used either singly or in any combination thereof.
Incidentally, a polymerization inhibitor may or may not be caused to
coexist in the monomer.
One or more of crosslinkable monomers, for example, aromatic divinyl
compounds such as divinylbenzene, divinylnaphthalene and derivatives
thereof; di- or tri-ethylenically unsaturated carboxylic acid esters such
as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate,
triethylene glycol dimethacrylate, trimethylolpropane triacrylate and
1,3-butanediol dimethacrylate; divinyl compounds such as
N,N-divinylaniline, divinyl ether, divinyl sulfide and divinyl sulfone;
and compounds having at least three vinyl groups, may be used together
with the above-mentioned vinyl monomers. These crosslinkable monomers are
generally used in a proportion of 0-20 wt. % based on the whole monomer
component including the vinyl monomers.
Colorant
As the colorant useful in the practice of the present invention, there may
be used pigments and dyes, for example, carbon black, aniline black,
Chalcoil Blue, chrome yellow, ultramarine blue, Orient Oil Red, crystal
violet, Rhodamine B, Malachite Green, Nigrosine, copper phthalocyanine and
azo dyes. These colorants may be used either singly or in any combination
thereof.
Metal oxides such as titanium oxide, silicon dioxide and zinc oxide; and
magnetic powders such as iron, cobalt, nickel, diiron trioxide, triiron
tetraoxide, manganese iron oxide, zinc iron oxide and nickel iron oxide
may also be used as the colorants. When a magnetic powder is used to
obtain polymer toner particles, finely divided powder having a particle
size of 1 .mu.m or smaller is preferably used.
Besides, high-polar substances referred to as the charge control agent in
this field, such as nigrosine dyes, monoazo dyes, metallized dyes, zinc
hexadecylsuccinate, alkyl esters or alkyl amides of naphthoic acid,
nitrohumic acid, N,N'-tetramethyldiamine benzophenone,
N,N'-tetramethylbenzidine, triazine and metal complexes of salicylic acid
may be used either singly or in any combination thereof.
No particular limitation is imposed on the amount of the colorant to be
used, and the amount varies according to the kind of the colorant to be
used. However, it is generally used in a proportion of about 0.1-200 parts
by weight per 100 parts by weight of the polymerizable monomer. In the
case of carbon black, about 1-20 parts by weight suffice.
Dispersing agent
Examples of the dispersing agent useful in the practice of the present
invention include water-soluble polymers such as gelatin and polyvinyl
alcohol; anionic dispersing agents disclosed in Japanese Patent
Application Laid-Open No. 123852/1984; and inorganic dispersing agents
such as hardly water-soluble metallic compounds.
Examples of the hardly water-soluble metallic compounds include compounds
which exhibit neutrality or alkalinity in water, such as calcium
phosphate, magnesium phosphate, calcium sulfate, magnesium carbonate,
calcium carbonate, calcium hydroxide and magnesium hydroxide; compounds
which exhibit acidity in water, such as aluminum phosphate, zinc phosphate
and zinc carbonate; and the like. The hardly water-soluble metallic
compound may be formed in situ. For example, when sodium phosphate is
reacted with calcium carbonate in water, a hardly water-soluble compound
is formed. Therefore, the resultant liquid reaction mixture may be used as
an aqueous dispersion medium containing the dispersing agent as it is.
In the present invention, it is preferable to use, as the dispersing agent,
colloid of a hardly water-soluble polyvalent metal hydroxide formed by the
reaction of a water-soluble polyvalent metal salt with an alkali metal
hydroxide in water. When the colloid of the hardly water-soluble
polyvalent metal hydroxide is used as the dispersing agent, the stability
of the droplets of the polymerizable monomer composition and the droplets
of the oil-soluble polymerization initiator does not become very high, so
that both droplet components are easy to unite with each other, and
uniform mixing is hence achieved with ease.
Examples of the water-soluble polyvalent metal salt include the
hydrochlorides, sulfates, nitrates and acetates of polyvalent metals such
as magnesium, calcium, aluminum, iron, copper, manganese, nickel and tin.
Of these, the use of the magnesium salts or calcium salts is preferred
from the viewpoint of dispersion stability. Examples of the alkali metal
hydroxide include lithium hydroxide, sodium hydroxide and potassium
hydroxide.
When a surfactant is added to the aqueous dispersion medium together with
the dispersing agent, the droplets of the polymerizable monomer
composition are easily made uniform. It is hence preferable to use the
dispersing agent in combination with the surfactant.
Oil-soluble polymerization initiator
As the oil-soluble polymerization initiator useful in the practice of the
present invention, may be mentioned peroxide-type initiators, azo-type
initiators and the like. The use of an initiator having a solubility in
water of 1 wt. % or lower is preferred from the viewpoint of achieving
good migration of the initiator to the droplets of the polymerizable
monomer composition when stirred in water.
As the oil-soluble polymerization initiator, there may be used any
oil-soluble initiator of the peroxide or azo type, which is generally used
in suspension polymerization. Specific examples thereof include
peroxide-type initiators such as benzoyl peroxide, octanoyl peroxide,
ortho-methoxybenzoyl peroxide, methyl ethyl ketone peroxide, cumene
hydroperoxide, t-butyl hydroperoxide and t-butyl peroxy-2-ethylhexanoate;
and azo-type initiators such as 2,2'-azobisisobutyronitrile,
2,2º'-azobis-(2,4-dimethylvaleronitrile),
2,2'-azobis-2,3-dimethylbutyronitrile,
2,2'-azobis-2,3,3-trimethylbutyronitrile,
2,2'-azobis-2-isopropylbutyronitrile, 4,4-azobis-4-cyanovaleric acid and
dimethyl 2,2'-azobisisobutyrate.
When an organic peroxide whose ten-hour half-life temperature is
60.degree.-80.degree. C. and whose molecular weight is 250 or lower is
used as the oil-soluble polymerization initiator, the odor of the
resulting polymer toner attributed to residual monomers can be reduced.
The term "ten-hour half-life temperature" as used herein means a
temperature at which the half-life of the organic peroxide comes to 10
hours. Specific examples of such organic peroxides include t-butyl
peroxy-2-ethylhexanoate, succinamide peroxide, t-hexyl
peroxy-2-ethylhexanoate and t-butyl peroxyisobutyrate.
The oil-soluble polymerization initiator is used in a proportion of
generally 0.01-20 parts by weight, preferably 0.1-10 parts by weight per
100 parts by weight of the polymerizable monomer.
Other additives
In the present invention, charge control agents such as Spiron Black TRH
(product of Hodogaya Chemical Co., Ltd.), Bontron S-34 (product of Orient
Chemical Industries Ltd.) and Nigrosine (product of Orient Chemical
Industries Ltd.); parting agents such as low-molecular weight
polyethylene, low-molecular weight polypropylene; molecular weight
modifiers such as t-dodecylmercaptan and n-dodecylmercaptan; and the like
may be added to the polymerizable monomer composition.
Production process of polymer toner
In the production process according to the present invention, a colorant
and optionally additives (for example, a charge control agent) other than
an oil-soluble polymerization initiator are added to a polymerizable
monomer, and these components are stirred and mixed to prepare a
polymerizable monomer composition comprising the individual components
dissolved or dispersed uniformly therein. After the composition is poured
into an aqueous dispersion medium containing a dispersing agent, the
oil-soluble polymerization initiator is added to the aqueous dispersion
medium with stirring. In this step, droplets of the polymerizable monomer
composition are brought into contact with droplets of the oil-soluble
polymerization initiator, so that both droplet components unite with each
other, whereby droplets of a polymerizable monomer composition containing
the oil-soluble polymerization initiator are formed.
In the present invention, the time the oil-soluble polymerization initiator
is added to the aqueous dispersion medium must be after the polymerizable
monomer composition is poured and in the course of forming droplets of the
polymerizable monomer component. When the oil-soluble polymerization
initiator is added after the polymerizable monomer composition is formed
into fine droplets having desired droplet sizes in the aqueous dispersion
medium, the oil-soluble polymerization initiator is difficult to uniformly
mix with such droplets.
The time the oil-soluble polymerization initiator is added is when the
droplet size (volume average droplet size) of the primary droplets formed
by the stirring after the pouring of the polymerizable monomer composition
comes to generally 50-1,000 .mu.m, preferably 100-500 .mu.m though the
time varies according to the intended particle size of the resulting
toner. When the period of time from the pouring of the polymerizable
monomer composition to the addition of the oil-soluble polymerization
initiator is long, the formation of the droplets has been completed, so
that the polymerizable monomer composition is not uniformly mixed with the
oil-soluble polymerization initiator, resulting in difficulty in making
resin properties such as polymerization degree and crosslinking degree
uniform at every polymer toner particle. Therefore, the time the
oil-soluble polymerization initiator is added is not longer than generally
24 hours, preferably 12 hours, more preferably 3 hours after the pouring
of the polymerizable monomer composition on a large scale such as plant,
or not longer than generally 5 hours, preferably 3 hours, more preferably
1 hour on a small laboratory scale though it somewhat varies according to
reaction scale and the intended particle sizes of the resulting toner.
The temperature of the aqueous dispersion medium between the time the
oil-soluble polymerization initiator is added and the subsequent formation
of droplets (namely, before initiation of polymerization) is controlled
within a range of generally 10.degree.-40.degree. C., preferably
20.degree.-30.degree. C. If the temperature is too high, a partial
polymerization reaction is started in the system. If the temperature is
too low on the other hand, the flowability of the system is reduced when
droplets are formed by stirring, resulting in possibility that it may
interfere with the formation of the droplets.
In the present invention, after the droplets of the polymerizable monomer
composition are brought into contact with the droplets of the oil-soluble
polymerization initiator to form droplets of a polymerizable monomer
composition containing the oil-soluble polymerization initiator, the
stirring is further continued to form secondary droplets having desired
droplet sizes, and suspension polymerization of the polymerizable monomer
composition is then conducted. In the step of forming the secondary
droplets, the secondary droplets are finely divided to such an extent that
in the subsequent suspension polymerization, a polymer toner having a
volume average particle size of generally about 1-50 .mu.m, preferably
about 5-30 .mu.m is formed. The time the secondary droplets are formed can
be optionally set according to the kinds and added amounts of the
polymerizable monomer, additives, polymerization initiator and the like,
temperature upon the formation of the droplets, the kind of a machine used
in the formation of the droplets, and desired droplet sizes. After the
conversion of the polymerizable monomer composition into a polymer exceeds
90%, the polymerizable monomer may be additionally added to continue the
polymerization. The continuation of the polymerization permits the
provision of toner particles of a capsule structure, by which shelf life
is improved.
After completion of the suspension polymerization, the resultant polymer is
thoroughly washed, dehydrated and dried to collect a polymer toner. When a
dispersing agent composed of the hardly water-soluble metallic compound is
used, an acid or alkali is added to the system containing a colored
particulate polymer (polymer toner) formed after completion of the
suspension polymerization to solubilize the dispersing agent composed of
the hardly water-soluble metallic compound, and the polymer is then
thoroughly washed, dehydrated and dried.
ADVANTAGES OF THE INVENTION
According to the present invention, there can be provided a polymer toner
homogeneous in the composition of toner particles and ununiform in resin
properties such as polymerization degree and crosslinking degree in
accordance with the suspension polymerization method. When the polymer
toner obtained by the production process according to the present
invention is used as a toner for developing electrostatic latent images in
electrophotographic copying machines and the like, bright prints free of
fog and scattering spots can be obtained, no offset is caused, and fixing
ability is also good.
EMBODIMENTS OF THE INVENTION
The present invention will hereinafter be described more specifically by
the following Examples and Comparative Examples. However, this invention
is not limited to these examples only.
EXAMPLE 1
Stirred and mixed at 6,000 rpm in a T.K. system homomixer (manufactured by
Tokushu Kika Kogyo Co., Ltd.), which is a mixer having high shearing
force, were 70 parts by weight of styrene, 30 parts by weight of butyl
methacrylate, 0.3 parts by weight of divinylbenzene, 8 parts by weight of
carbon black ("Printex 150T", trade name, product of Degussa AG; particle
size: 29 nm) and 0.5 parts by weight of a Cr dye ("Bontron S-34", trade
name, product of Orient Chemical Industries Ltd.), thereby obtaining a
polymerizable monomer composition uniformly dispersed.
On the other hand, an aqueous solution with 6.9 parts by weight of sodium
hydroxide dissolved in 50 parts by weight of ion-exchanged water was
gradually added to an aqueous solution with 9.8 parts by weight of
magnesium chloride dissolved in 250 parts by weight of ion-exchanged water
under stirring, thereby preparing a liquid colloidal dispersion of
magnesium hydroxide.
The polymerizable monomer composition was then poured into the liquid
colloidal dispersion of magnesium hydroxide obtained above, and the
temperature of the system was maintained at 20.degree.-30.degree. C. while
stirring for 2-3 minutes at a low speed by means of the T.K. system
homomixer. At the time primary droplets having a volume average droplet
size of about 200 .mu.m were formed, 2 parts by weight of
2,2'-azobisisobutyronitrile were added. The resultant mixture was further
stirred at 8,000 rpm by means of the T.K. system homomixer until secondary
droplets having a volume average droplet size of about 5 .mu.m were
formed. After completion of the step of forming the secondary droplets,
the aqueous dispersion containing the secondary droplets of the
polymerizable monomer composition containing the initiator was placed in a
1-liter 4-necked flask equipped with a stirrer, thermometer, nitrogen
inlet tube and reflux condenser to polymerize the monomer composition
under stirring for 8 hours at 65.degree. C.
After the thus-obtained polymer dispersion was thoroughly washed with an
acid and water, the resultant polymer was separated and dried to obtain a
colored particulate polymer (polymer toner).
The particle size of the thus-obtained polymer toner was measured by a
Coulter counter (manufactured by Coulter Co.) and found to be 9.0 .mu.m in
terms of volume average particle diameter (dv).
This polymer toner was evaluated by using a commercially-available printer
of an electrophotographic system. As a result, bright prints free of fog
and scattering spots were obtained though they somewhat gave off odor. In
addition, no offset was caused, and fixing ability was also good. The
amount of monomers remaining in the polymer toner was measured by means of
gas chromatography. As a result, it was found to be 710 ppm.
Comparative Example 1
Stirred and mixed at 6,000 rpm in a T.K. system homomixer (manufactured by
Tokushu Kika Kogyo Co., Ltd.), which is a mixer having high shearing
force, were 70 parts by weight of styrene, 30 parts by weight of butyl
methacrylate, 0.3 parts by weight of divinylbenzene, 8 parts by weight of
carbon black ("Printex 150T", trade name, product of Degussa AG) and 0.5
parts by weight of a Cr dye ("Bontron S-34", trade name, product of Orient
Chemical Industries Ltd.), thereby obtaining a polymerizable monomer
composition uniformly dispersed.
On the other hand, an aqueous solution with 6.9 parts by weight of sodium
hydroxide dissolved in 50 parts by weight of ion-exchanged water was
gradually added to an aqueous solution with 9.8 parts by weight of
magnesium chloride dissolved in 250 parts by weight of ion-exchanged water
under stirring, thereby preparing a liquid colloidal dispersion of
magnesium hydroxide.
The polymerizable monomer composition was then poured into the liquid
colloidal dispersion of magnesium hydroxide obtained above, and the
resultant mixture was subjected to high-shear stirring at 8,000 rpm by
means of the T.K. system homomixer while maintaining the temperature of
the system at 20.degree.-30.degree. C., thereby forming droplets of the
polymerizable monomer composition having a volume average droplet size of
about 5 .mu.m.
After completion of the step of forming the droplets, 2 parts by weight of
2,2'-azobisisobutyronitrile were added to the aqueous dispersion
containing the droplets of the polymerizable monomer composition, and the
resultant mixture was placed in a 1-liter 4-necked flask equipped with a
stirrer, thermometer, nitrogen inlet tube and reflux condenser to
polymerize the monomer composition under stirring for 8 hours at
65.degree. C.
After the thus-obtained polymer dispersion was thoroughly washed with an
acid and water, the resultant polymer was separated and dried. However,
particles of the polymer aggregated in the drying step, so that no
satisfactory colored particulate polymer (polymer toner) could be
obtained. The amount of monomers remaining in this aggregate was very
large, and it is hence considered that the polymerization reaction was not
completed because the dispersion of the polymerization initiator was
uneven.
Comparative Example 2
Stirred and mixed at 6,000 rpm in a T.K. system homomixer (manufactured by
Tokushu Kika Kogyo Co., Ltd.), which is a mixer having high shearing
force, were 70 parts by weight of styrene, 30 parts by weight of butyl
methacrylate, 0.3 parts by weight of divinylbenzene, 8 parts by weight of
carbon black ("Printex 150T", trade name, product of Degussa AG), 0.5
parts by weight of a Cr dye ("Bontron S-34", trade name, product of Orient
Chemical Industries Ltd.) and 2 parts by weight of
2,2'azobisisobutyronitrile, thereby obtaining a polymerizable monomer
composition uniformly dispersed.
On the other hand, an aqueous solution with 6.9 parts by weight of sodium
hydroxide dissolved in 50 parts by weight of ion-exchanged water was
gradually added to an aqueous solution with 9.8 parts by weight of
magnesium chloride dissolved in 250 parts by weight of ion-exchanged water
under stirring, thereby preparing a liquid colloidal dispersion of
magnesium hydroxide.
The polymerizable monomer composition containing the oil-soluble
polymerization initiator prepared above was then poured into the liquid
colloidal dispersion of magnesium hydroxide obtained above, and the
resultant mixture was subjected to high-shear stirring at 8,000 rpm by
means of the T.K. system homomixer while maintaining the temperature of
the system at 20.degree.-30.degree. C., thereby forming droplets of the
polymerizable monomer composition having a volume average droplet size of
about 5 .mu.m.
The aqueous dispersion containing the droplets of the polymerizable monomer
composition was placed in a 1 liter 4-necked flask equipped with a
stirrer, thermometer, nitrogen inlet tube and reflux condenser to
polymerize the monomer composition under stirring for 8 hours at
65.degree. C.
After the thus-obtained polymer dispersion was thoroughly washed with an
acid and water, the resultant polymer was separated and dried to obtain a
colored particulate polymer (polymer toner).
The particle size of the thus-obtained colored fine particles was 9.8 .mu.m
in terms of volume average particle size. However, fine and coarse powders
were generated in plenty, and so the particle size distribution of the
toner obtained was wide. This is considered to be attributable to the fact
that polymerization is partially started during the high-shear stirring of
the polymerizable monomer composition, resulting in increase in viscosity
of the polymerizable monomer composition.
EXAMPLE 2
An experiment was performed in the same manner as in Example 1 except that
t-butyl peroxy-2-ethylhexanoate was used as the oil-soluble polymerization
initiator in place of 2,2'-azobisisobutyronitrile in Example 1.
The particle size of the thus-obtained polymer toner was measured by a
Coulter counter (manufactured by Coulter Co.) and found to be 6.8 .mu.m in
terms of volume average particle diameter (dv). This polymer toner was
evaluated by using a commercially-available printer of an
electro-photographic system. As a result, bright prints free of fog and
scattering spots were obtained without giving off odor. In addition, no
offset was caused, and fixing ability was also good. The amount of
monomers remaining in the polymer toner was measured by means of gas
chromatography. As a result, it was found to be 240 ppm.
EXAMPLE 3
An experiment was performed in the same manner as in Example 1 except that
t-butyl peroxy-2-ethylhexanoate was used as the oil-soluble polymerization
initiator in place of 2,2'-azobisisobutyronitrile in Example 1, and was
added at the time the volume average droplet size of the primary droplets
of the polymerizable monomer composition came to 300 .mu.m.
The particle size of the thus-obtained polymer toner was measured by a
Coulter counter (manufactured by Coulter Co.) and found to be 7.0 .mu.m in
terms of volume average particle diameter (dv). This polymer toner was
evaluated by using a commercially-available printer of an
electro-photographic system. As a result, bright prints free of fog and
scattering spots were obtained without giving off odor. In addition, no
offset was caused, and fixing ability was also good. The amount of
monomers remaining in the polymer toner was measured by means of gas
chromatography. As a result, it was found to be 400 ppm.
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